System and method for efficiently allocating wireless resources

ABSTRACT

Dynamic resource allocation is performed by first generating a plurality of slot sequences. A figure of merit based on weighted interference signal code power (ISCP) and weighted resource units is then generated for each timeslot of each slot sequence. The timeslots within each slot sequence are then arranged in a decreasing figure of merit. The slot sequences are the processed to determine whether they can support the code to be transmitted.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional application No.60/494,878, filed on Aug. 13, 2003, which is incorporated by referenceas if fully set forth.

FIELD OF INVENTION

The present invention relates to wireless communication systems. Moreparticularly, the present invention relates to a method for resourceallocation in a wireless communication system.

BACKGROUND

All known communication standards impose limits on the use of systemresources, regardless of the type of resources that are allocated.Resource management is used in communication systems to effectivelyallocate the limited amount of system resources to all users. Suchresources may include timeslots, RF carriers or codes. For example, theUniversal Mobile Telecommunication System (UMTS) Time Division Duplex(TDD) standards define a single carrier cell that includes a beacon andother common channels and timeslots. Accordingly, in this case, carrierselection is equivalent to cell selection.

In contrast, the China Wireless Telecommunication Standard (CWTS) groupTime Division Synchronous Code Division Multiple Access (TD-SCDMA)System for Mobile (TSM) standard defines a multi-carrier cell. However,it requires that all physical channels that belong to a singleapplication be assigned to the same carrier.

A generic multi-carrier TDD system can assign physical resources for aWireless Transmit/Receive Unit (WTRU) in different timeslots ofdifferent carriers. For example, the Fast Dynamic Channel Allocation(F-DCA) algorithm is used to allocate resources (i.e. which timeslots onwhich carrier) for a user which is referred as a coded composite trafficchannel (CCTrCH). This allocation is based on optimization of theassignment quality metric, which can be expressed as a combination of atimeslot-based assignment metric and a fragmentation metric for thewhole CCTrCH. In a timeslot-based assignment metric, timeslotinterference, timeslot transmit power, or timeslot loading is used. Inthe fragmentation metric for the whole CCTrCH, a fragmentation penaltyof using multiple timeslots within one carrier is assigned, or afragmentation penalty of using multiple carriers is assigned. LetTS_Frag_Penalty(j) denote the timeslot-based fragmentation penalty whenj timeslots are used. For example, TS_Frag_Penalty(j) is defined as:$\begin{matrix}{{{TS\_ Frag}{\_ Penalty}(j)} = \left\{ {\begin{matrix}{p \cdot \left( {j - 1} \right)} & {{{if}\quad 0} < j \leq C} \\\infty & {{{{if}\quad j} > C}\quad}\end{matrix};} \right.} & {{Equation}\quad(1)}\end{matrix}$where p is the timeslot-based fragmentation penalty increment, and C isthe maximum number of time slots that a user can support.

Let Carrier_Frag_Penalty(j) denote the carrier-based fragmentationpenalty when j carriers are used. For example, Carrier _Frag_Penalty(j)is defined as:Carrier_Frag_Penalty(j)=q·(j−1);  Equation (2)where q is the carrier-based fragmentation penalty increment.

Although some WTRUs may use multiple receivers and have noimplementation constraints on slot selection, most WTRUs have a singlereceiver and a finite switching time between uplink (UL) and downlink(DL) timeslots. Therefore, for most WTRUs, when timeslots from more thanone carrier are used, the following two limitations apply: 1) if atimeslot is used by the WTRU in one carrier, the same timeslot cannot beused by the WTRU in other carriers; and 2) if a timeslot is used by theWTRU in one carrier, only timeslots that allow enough guard time apartfrom the used timeslot for the WTRU transceiver to switch frequenciescan be used by the same WTRU in other carriers.

Those timeslots that cannot be used because of the usage of a particulartimeslot and the two aforementioned limitations are defined as the setof banned timeslots of the particular timeslot.

Although channel allocation algorithms have been developed for TDDsystems, these systems typically compromise a single carrier used by anoperator. In multi-carrier TDD systems, the network has the freedom toassign the WTRU to one or several carriers. Therefore, there exists aneed to properly allocate resources for multi-carrier TDD systems.

SUMMARY

According to the present invention, dynamic resource allocation isperformed by first generating a plurality of slot sequences. A figure ofmerit based on weighted interference signal code power (ISCP) andweighted resource units (RUs) is then generated for each timeslot ofeach slot sequence. The timeslots within each slot sequence are arrangedin a decreasing figure of merit. The slot sequences are then processedto determine whether they can support the code to be transmitted.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIGS. 1A and 1B taken together are a flow diagram of a method inaccordance with the present invention.

FIG. 2 is a block diagram of a multiple carrier communication system inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention will be described with reference to the drawingsfigures where like numerals represent like elements throughout.

The preferred embodiments of the present invention are described inconjunction with a communication system supporting voice and datatransmissions according to the Third Generation Partnership Project(3GPP) wideband code division multiple access (W-CDMA) communicationsystem. However, it should be noted that the 3GPP system is used only asan example and the invention can be applied to other CDMA systems. Whilethe exemplary embodiments are described in terms of wireless spreadspectrum communications, the invention can be applied to other forms ofslotted, non-slotted, multicarrier and single carrier communicationsystems, and can be applied broadly to all types of communicationformats. In addition, the invention can be applied to communicationswhich are wireless and which use hardwire connections. Whilebase-to-mobile transmissions have been described, the inventive conceptsare also useful in peer-to-peer communications.

As used herein, the term WTRU includes, but is not limited to, a userequipment, mobile station, fixed or mobile subscriber unit, pager or anyother type of device capable of operating in a wireless environment.These exemplary types of wireless environments include, but are notlimited to, wireless local area networks (WLANs) and public land mobilenetworks (PLMNs). The term base station, as used hereinafter, includes,but is not limited to, a Node B, site controller, access point or otherinterfacing device in a wireless environment.

According to an exemplary aspect of the present invention using the TSMstandard, an improved resource allocation procedure is implemented. TheTSM standard requires that all physical channels that belong to a singleapplication be assigned to the same carrier. The resource allocationprocedure in accordance with the present invention is performed for eachcarrier. Then, among all carriers, a selection is made of the carrierthat yields the best assignment quality metric.

To support a CCTrCH in a generic multi-carrier TDD system, several codesare needed. Usually, those codes are arranged in the order of increasingspreading factor of the code. This arrangement of codes is called a codeset. As understood by those of skill in the art, the lower the spreadingfactor of a code, the more RUs that are required to transmit the code.

Referring to FIG. 1, a dynamic resource allocation procedure 100 inaccordance with the present invention is shown. The procedure 100 beginsat step 10, whereby a plurality of slot sequences are generated. Theslot sequences, which are a group of timeslots in a specific order, aregenerated by applying k+m+1 pairs of α and β values according toα^((k))=1β^((k))=2^(k) (sequence k+1) and α^((k+m+1))=2^(m)β^((k+m+1))=1 (sequence k+m+1); where α is the weight parameter of ISCPand β is the weight parameter of the number of RUs that can used by theCCTrCH in the slot.

By applying k+m+1 pairs of α and β values, k+m+1 slot sequences, aregenerated as follows:

-   -   a) Since α is kept equal to 1 and β is increased, the following        sequences favor low fragmentation:        α⁽¹⁾=1 β⁽¹⁾=2⁰ (sequence 1),        α⁽²⁾=1 β⁽²⁾=2¹ (sequence 2),        α⁽³⁾=1 β⁽³⁾=2² (sequence 3),    -    so that,        α^((k))=1 β^((k))=2^(k) (sequence k+1).  Equation (3)    -   b) Since β is kept equal to 1 and α is increased, the following        sequences favor low interference:        α^((k+1))=2¹ β^((k+1))=1 (sequence k+2),        α^((k+2))=2² β^((k+2))=1 (sequence k+3),    -    so that,        α^((k+m+1))=2^(m) β^((k+m+1))=1 (sequence k+m+1).  Equation (4)

A figure of merit Fi is then computed for each timeslot (step 11). Thefigure of merit Fi of slot i is generated as:F _(i) =−α·Δl _(i) α·f(C _(i));  Equation (5)where Δl_(i) is defined as ISCP_(i)−ISCP_(min); ISCP_(j) is the measuredinterference signal code power ISCP (in dB) in the slot i; ISCP_(min) isthe lowest ISCP (in dB) among all available timeslots in the samedirection (i.e., UL or DL); and f(C_(i)) is the amount of RUs that canbe used by the CCTrCH of interest in the slot i.

The parameter f(C_(i)) is calculated as:f(C _(i))=min(C _(i), min(M, RU _(max) _(—) _(slot))),  Equation (6)where C_(i) is the number of available RUs in the slot i; M is theamount of resource units required by the CCTrCH; and RU_(max) _(—)_(slot) is the maximum amount of RUs that can be used by this CCTrCH inone slot.

Assuming that the WTRU is supporting m CCTrCHs (where m≧1)simultaneously and that the number of codes used by other CCTrCHs ofthis WTRU in this timeslot is N_(USED), since the WTRU has a capabilityof N_(WTRU) codes per timeslot, the number of codes that this CCTrCH canuse in this timeslot is N_(WTRU)−N_(USED). Therefore, RU_(max) _(—)_(slot) is given by the highest amount of RUs that can be used byN_(WTRU)−N_(USED) codes in the CCTrCH.

The timeslots of each slot sequence are then arranged in the order ofdecreasing figure of merit F_(i) (step 12). This provides an arrangedslot sequence.

Beginning with the first slot sequence (step 14) the first timeslot inthe first slot sequence is selected (step 16). The code with thesmallest spreading factor in the code set is also selected (step 18)since this will require the most RUs.

It is determined if there is a code with corresponding spreading factoravailable in the selected timeslot (step 20). If so, (i.e. the code isavailable and the assignment does not violate any capability of theWTRU, for example, the maximum number of time slots that can be used bya WTRU), and the procedure advances to step 23.

If the determination in step 20 is negative (i.e. a corresponding codeis not available or the assignment violates some of the capabilities ofthe WTRU), then the action depends on whether it is an UL timeslot or aDL timeslot (step 24). If it is an UL timeslot, the procedure 100advances to step 26. If it is a DL timeslot, the procedure 100 advancesto step 28 since in the DL all codes have the same spreading factor andif the present code cannot be supported in the timeslot, none of theremaining unassigned codes would be able to be supported in thetimeslot.

At step 26, it is determined if there is a code with a higher spreadingfactor in the code set. If so, the code from the code set with the nextlarger spreading factor is selected (step 30) and the procedure 100reverts back to step 20. If a code from the code set with a higherspreading factor is not available, the procedure 100 advances to step28, where the present timeslot is eliminated from the sequence oftimeslots and the slot sequence is updated.

If there are any more timeslots left in the sequence (step 32), the nexttimeslot in the slot sequence is tried and a timeslot counter, which isinitialized at the beginning of the analysis of each slot sequence, isupdated (step 34). If there are no more timeslots left in the sequenceas determined at step 32, no slot assignment solution can be found forthis slot sequence (step 38).

It is then determined whether any more slot sequences are available(step 40). If so, the next slot sequence is selected (step 42) and theISCP of each timeslot is reset. The procedure 100 then reverts back tostep 16.

At step 36, it is determined whether the total number of timeslots thatwould be needed if this timeslot were to be used for the CCTrCH iswithin the capability of the WTRU. For example, some WTRUs may only beable to support a certain number of timeslots. An assignment solutionthat uses more timeslots than that number will automatically fail. Ifthe total number of timeslots is within the capability of the WTRU, theprocedure 100 reverts back to step 20. If the total number of timeslotsit is not within the capability of the WTRU, the CCTrCH cannot beassigned to more timeslots and no slot assignment solution can be foundfor this slot sequence (step 38). The procedure 100 then advances tostep 40.

Referring back to step 20, if the determination at step 20 isaffirmative, an estimate is made of the noise rise and code transmitpower in the timeslot if a code with this spreading factor is added(step 23). It is then determined if this spreading factor can besupported in the timeslot (step 44). This determination is made suchthat if the estimated noise rise and transmission power violates any ofthe following requirements, this spreading factor cannot be supported inthis slot:

-   -   1. Noise rise cannot exceed a pre-determined threshold. The        threshold is a design parameter.    -   2. Interference (ISCP) cannot exceed a pre-determined threshold.        The threshold is a design parameter.    -   3. In the UL, WTRU transmission power cannot exceed its maximum        allowed UL transmit power, (i.e. sum of transmit power of all        codes for that UE in that timeslot).    -   4. In the DL, Node-B carrier power cannot exceed it's maximum        transmit power defined by the power class, (i.e. sum of        transmission power of all codes for all WTRUs in that timeslot).    -   5. In the DL, the difference between the code transmit power of        any two codes in the same timeslot cannot exceed the maximum        dynamic range. The value of maximum dynamic range is a design        parameter.

If this code (i.e. the spreading factor) cannot be supported in thetimeslot as determined at step 44, the procedure 100 advances to step28.

If the code can be supported in the timeslot, the procedure 100 advancesto step 46 where the interference in the timeslot is updated. The slotsequence is updated by deleting all timeslots that cannot be used inother carriers because of the usage of this timeslot.

It is then determined whether any more codes need to be assigned, (i.e.,if there are any codes left in the code set (step 48)). If so, theprocedure 100 advances to step 50 and an attempt is made to assign thenext code in the code set into this timeslot. It should be noted that inthis estimate, the ISCP should take the updated value.

If all codes have been assigned (step 48), an assignment solution hasbeen found (step 52). This assignment solution is recorded for this slotsequence, (i.e. the number of codes and their spreading factors for eachused timeslot within each used carrier). Assuming that the CCTrCH uses Ncarriers, and within each carrier n, S_(n) timeslots are used,ISCP_(total)(n) denotes the total interference of the CCTrCH in carriern. The weighted interference, ISCP_(weighted), is computed as totalinterference plus timeslot fragmentation penalty and carrierfragmentation penalty: $\begin{matrix}{{ISCP}_{weighted} = {\left( {{\sum\limits_{n = 1}^{N}{{ISCP}_{total}(n)}} + {{TS\_ Frag}{\_ Penalty}\left( S_{n} \right)}} \right) + {{Carrier\_ Frag}{\_ Penalty}{(N).}}}} & {{Equation}\quad(7)}\end{matrix}$

If there are more slot sequences as determined at step 40, the next slotsequence is selected and the ISCP is reset to the ISCP of the first slotof the selected slot sequence. The procedure 100 then reverts back tostep 16. In this way, other assignment solutions will be found, eachwith their corresponding weighted interference. If the slot selectionfor all the slot sequences has been performed as determined at step 40,it is determined if at least one sequence generated an assignmentsolution (step 54). If not, no assignment solution has been found interms of power/interference availability and the procedure 100 iscompleted (step 58). If at least one assignment solution is found, theone with the lowest weighted interference among all assignment solutionsis selected as the optimal assignment solution. The procedure 100 iscompleted (step 58).

FIG. 2 is a general configuration of a wireless communication system 200which includes a core network 202, and a plurality of mobile WTRUs 204,206. The network 202 includes a radio network controller (RNC) 210,coupled to a Node B 212, which is further coupled to a plurality of basestations 214, 216, 218. In operation, the network 202 communicates withthe WTRUs 204, 206 through base stations 208. Each WTRU 204, 206 includea, transceiver section 222 and a signal processing section 220 which,among other factors, assigns communications slots. In one embodiment,the procedure shown in FIG. 1 is performed at the RNC for dedicatedchannels, and performed at Node B for shared channels. For an ad hocnetwork, (such as WLAN), such a procedure can be performed at the WTRU.

1. A method for allocating timeslots in a time-slotted communicationsystem to support transmission of a plurality of codes in a code set;the method comprising: generating a plurality of slot sequencesutilizing at least one selectively weighted value, each slot sequencecomprising a plurality of timeslots; calculating a figure of merit foreach timeslot, the figure of merit being based, at least in part, uponsaid selectively weighted value; arranging said plurality of timeslotswithin each said slot sequence in order of a decreasing figure of meritto provide an arranged slot sequence; and comparing each of saidplurality of codes within said code set to each said arranged slotsequence to determine whether said arranged slot sequence can supportsaid code set and, if so, identifying the slot sequence as an assignmentsolution.
 2. The method of claim 1, further comprising calculating aweighted interference value for each assignment solution.
 3. The methodof claim 2, further comprising selecting the assignment solution withthe lowest weighted interference as the optimal solution.
 4. The methodof claim 1, wherein said at least one selectively weighted valuecomprises a weighted parameter related to interference signal code power(ISCP) a and a weight parameter related to the number of resource units(RUs) that can be used in a particular timeslot.
 5. The method of claim1, wherein the plurality of codes within said code set have a pluralityof different spreading factors.
 6. The method of claim 5, wherein saidcomparing step further comprises: selecting the code within the code setwith the smallest spreading factor; selecting a timeslot in the arrangedslot sequence; determining whether there is a code available in theselected timeslot to support the smallest spreading factor and, if so,identifying the code as an available code.
 7. The method of claim 6,wherein said comparing step further comprises: estimating the noise riseand transmit power of the selected timeslot if the available code isassigned to the selected timeslot; and determining if noise rise andtransmit power in the selected timeslot are excessive.
 8. The method ofclaim 7, wherein said comparing step further comprises: updating theinterference in the selected timeslot if the noise rise and transmitpower in the selected timeslot are not excessive.
 9. The method of claim7, wherein said comparing step further comprises: updating the slotsequence by deleting timeslots that cannot be used because of the use ofthe selected timeslot if the noise rise and transmit power in theselected timeslot are not excessive.